Flywheel magneto assembly for internal combustion engines



y 9, 1939- E. N. JACOB! 2,157,666

FLYWHEEL MAGNETO ASSEMBLY FOR INTERNAL COMBUSTION ENGINES Filed Sept. 16, 1936 2 Sheets-Sheet l EJWPJM Jami?! guwg I CW E. N. JACOB! 2,157,666

FLYWHEEL MAGNETO ASSEMBLY FOR INTERNAL COMBUSTION ENGINES May 9, 1939.

Filed Sept. 16. 1936 2 Sheets-Sheet 2 $440M Edward All/7500171 POINTS OPEN PO/NTS 0.051;"

Patented May 9, 1939 UNITED STATES PATENT OFFICE FLYWHEEL MAGNETO ASSEIHBLY FOR INTERNAL COMBUSTION ENGINES Edward N. Jacobi, Milwaukee, Wis., assignor to Briggs & Stratton Corporation,

Milwaukee,

2 Claims.

This inventionrelates to improvements in internal combustion engines'and refers particularly to the magneto assemblies therefor.

It is an object of this invention to provide an improved magneto of the fly-wheel type whereby the size of the fly-wheel carried ring magnet may be proportioned to the magnetic requirements without regard for other factors.

It is another object of this invention to provide a magneto assembly of the fly-wheel type in which the coil and its armature core are mounted wholly outside the fly-wheel.

Another object of this invention is to provide a magneto assembly of the character described in which the coil and its core are so located as to be cooled by the air flow induced by the flywheel impeller so that eflicient heat dissipation is obtained with a minimum use of copper and iron.

It is also an object of this invention to provide a magneto assembly which so disposes its ignition coil that the lead to the spark plug is exceptionally short.

Another object of this invention is to provide a magneto assembly wherein a quick reversal is obtained in the direction of flux flowing through the armature core upon which the coil is mounted.

More specifically, it is an object of this invention to provide a magneto assembly wherein a three legged armature core is employed Whose dimensions are such with respect to the poles of the ring magnet as to insure a very rapid change in the direction of flux flowing in the center leg upon which the coil is mounted.

With the above and other objects in view which will appear as the description proceeds, this invention resides in the novel construction, combination and arrangement of parts substantially as hereinafter described and more particularly defined by the appended claims, it being understood that such changes in the precise embodiment of the herein disclosed invention may be r made as come within the scope of the claims.

The accompanying drawings illustrate a complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:

Figure l is a side view of an internal combustion engine with parts broken away and in section showing this invention;

Figure 2 is an end view of the engine with parts broken away and in section; and

' site the center of the air impeller 15.

Figures 3 and 4 are detail views showing the manner in which the direction of flux is abruptly changed.

Referring now particularly to the accompanying drawings, in which like numerals indicate like parts throughout the several views, the numeral 5 designates the crank case of a small portable combustion engine upon which a cylinder 6 is mounted. Ordinarily, the cylinder and the crank case are cast in one unit. The top of the cylinder is closed by a cylinder head 1 in which a spark plug 8 is secured. One end of the crank case is closed by a plate 9 and its opposite end is closed by a mounting plate |0.' The plates 9 and lil have crank shaft bearings l I and 12, respectively, in which the crank shaft 13 of the engine is journaled.

Outwardly of the mounting plate Hi the crank shaft mounts a fiy-wheel I4, on the outer face of which is an air impeller l5 to induce a flow of cooling air as hereinafter more fully described.

'REISSUED DEC 3 1 1940 Imbedded in the fly-wheel is a permanentring Y magnet [6 having pole pieces I! and I8 spaced apart a short distance and exposed at the outer periphery of the wheel.

The lower portion of the mounting plate is circular and substantially co-extensive in size with the fly-wheel. Its upper portion is extended tangentially to provide an extension [9 alongside the cylinder 6 and reaching up to the head 1.

The mounting plate with its upward extension l9 forms the inner Wall of a blower housing and air guide 20, the other walls of which are formed by a stamped metal hood 2| which has a flat outer wall 22 of a size and shape roughly coextensive with that of the mounting plate, and integral side walls 23 which extend inwardly to engage the peripheral edge of the mounting plate at all portions except one upper corner. This corner of the plate is cut away as at 24 to define an outlet for the cooling air induced to flow through the housing by the impeller IS. The opening 24 is so located that the air issuing therefrom impinges the cylinder 6.

An inlet opening 25 to the blower housing and air guide 20 is formed in the outer wall 22 oppo- Consequently, air is drawn in through the opening 25 and blown out through the opening 24.

In the space within the housing 20 above the fly-wheel and alongside the outlet opening 24 so as to be located in the direct path of the cooling air is a magneto assembly indicated generally by the numeral 26. The assembly 26 comprises a three legged armature core 21 having a center leg 28 and side legs 29 and 38. The core, as is customary, is preferably laminated and is mounted by posts 3| on the outer face of the mounting plate extension I9 in a position with the lower curved end faces of its three legs 28, 29, and 30 lying in an arc concentric to and slightly spaced from the outer periphery of the fly-wheel. Consequently, the pole pieces I! and I8 successively sweep past the legs 29, 28, and 38 to induce a magnetic flux which is abruptly and rapidly reversed in direction through the center leg 28.

Mounted on the center leg is a conventional induction coil 32 having a primary and secondary. The coil is slipped onto the center leg 28 where it is held by spring retaining member 32'. Inasmuch as the three legs of the core are parallel and lie sufliciently close together so as to obviate the necessity for inwardly projecting horns on the outer legs 29 and 30, assembly of the coil freely onto and off of the center leg.

To obtain correct air gaps between the magnet poles [8 and I1 and the coil core poles 28, .29, and 30, it is only necessary to slide the coil core downward against feeler gauges held between the coil core poles and the flywheel periphery, and with the coil core held in this manner tighten its fastening screws.

One end of the primary and seconary of the coil is grounded as at 33. The other end of the secondary is connected through the customary high tension lead with the spark plug; and the other end of the primary is connected through a conductor 34 with an insulated terminal 35 of a circuit breaker. The other terminal of the circuit breaker is grounded and is also connected to a condenser 36 in the customary manner. The circuit breaker is adapted to be actuated by a pusher pin 31, which rides on the crank shaft in line with a flattened portion 38 so that the pin is permitted to descend and allow closure of the circuit breaker once each revolution.

It is to be observed that all of the instrumentai ities of the magneto are mounted on the outer face of the mounting plate where they are readily accessible, especially the coil and its armature core. It is also to be noted that this disposition of the coil and its core locates the same at a substantial elevation above the base where it is more likely to be clean and free from oil, and being mounted outside the flywheel and in position to be impinged by the cooling air, adequate heat dissipation is obtained with a minimum use of copper and iron.

In this respect it is to be observed that the coil and its core are so mounted on the plate l9 as to lie alongside or adjacent to the side of the main air stream issuing from the blower and passing to the outlet opening 24. One side of the coil core thus forms a guide or wall extending along one side of the main air stream so as to be cooled directly thereby. It is also to be observed that the curved bottom wall and tangential side wall of the blower housing, together with the coil defines substantially a scroll casing for the centrifugal impeller, and while the main air stream flows through this casing between the coil core and adjacent side wall of the housing to issue from the opening 24 and directly impinge the valves which are at the hottest portion of the engine, other lesser air streams flow through and over the coil and also past the other side of h the coil core to impinge the cylinder head.

Moreover, being mounted near the top of the mounting plate near the cylinder head, the high tension lead to the spark plug may be exceptionally short.

Another advantage of the present construction resides in the fact that the mounting plates besides carrying the magneto assembly also forms one wall of the blower housing air guide, thus reducing the number of parts; and with the coil and its core mounted outside the fly-wheel, the size of the ring magnet can be proportioned to the magnetic requirements without regard for the necessity of enclosing a bulky coil. This permits making the flywheel smaller in diameter and in turn allows the engine to be built much lower than in past constructions, as the fly-wheel when proportioned to the requirements of the length of the magnet bar needed for permanence is much smaller and much more economical of the material both in the magnet and in fly-wheel proper than in a construction where thesize of the flywheel is determined by mechanism which it must enclose. Also, of particular importance is the fact that a three legged armature core is employed, for through its use a more eificient magnetic machine is obtained.

As will be readily apparent particularly from Figures 3 and 4, the flux through the center leg 28 reverses abruptly and rapidly as the pole pieces rection of the magnetic flux through the center leg 28 and consequently the coil.

In this respect, attention is directed to the fact that the arcuate length of the two magnet pole pieces I! and I8 is suiiicient to span the distance between adjacent legs of the armature core and that the space between the pole pieces I1 and I8 is less than or at least not greater than the arcuate length of the pole face of the center leg 28. This dimensional relationship is responsible for the exceptional rapidity of the change in direction of flux for-as will be readily apparent from Figures 3 and 4, the flux flowing in one direction (Figure 3) hangs on and continues to flow in this direction until the very instant that the flux begins to flow in the opposite direction (Figure 4).

From the foregoing description taken in connection with the accompanying drawings, it will be readily apparent to those skilled in the art, that this invention provides an exceptionally compact and magnetically eflicient magneto assembly for small portable internal combustion engines.

What I claim as my invention is:

1. In a magneto assembly for an internal combustion engine having a crankcase, a crankshaft and a cylinder mounted on the crankcase, a plate closing one side of the crankcase and having a part projecting alongside the cylinder, a bearbetween the cylinder and the armature coil core. said core having limbs providing poles in close juxtaposition to the path of the magnet poles to be swept thereby as the flywheel revolves.

2. A'magneto assembly for an internal combustion engine having a crankcase with a crankshaft therein and a cylinder mounted on the crankcase, a flywheel on the crankshaft having its side which faces the crankcase hollowed to provide a cavity, a. permanent magnet carried by the flywheel with its poles facing the exterior of the flywheel rim, magneto parts inside the flywheel cavity including a "circuit breaker for the magneto primary circuit, a cam rotatable with the crankshaft, a-pusher pin operable by the cam to actuate the circuit breaker, an armature coil core having spaced limbs providing poles adapted to be swept by the poles of the permanent magnet, a plate closing the crankcase and the cavity formed by the hollow of the fly-wheel and having bores providing bearings for the crankshaft and the pusher pin and extending beyond the rim of the flywheel alongside the cylinder to provide a heat barrier between the-cylinder and the armature coil core, and means for mounting the core on said extending portion of the plate.

EDWARD N. JACOBI. 

